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Controlled Growth of Cu2ZnSnS4 (CZTS) Thin Films for Heterojunction Solar-cell Applications
INAMDARAKBAR IBRAHIM,Ki-Young Jeon,우현석,정웅,임현식,김형상 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10
Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB> (CZTS) thin films (absorber layers) were successfully synthesized on glass substrates using RF magnetron sputtering system. The films were rapidly thermally annealed to improve the crytallinity in a nitrogen atmosphere for 20 minutes. The formation of kesterite structures (JCPDS-26-0575) in the film was confirmed using X-ray diffraction (XRD) measurements. The improved crytallinity of the CZTS with a (112) orientation was observed with increasing annealing temperature. The band gap of the all these as-deposited and annealed films was found to be in the range of 1.97 to 1.55 eV. The films stoichiometry and morphology were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) measurements. The sample annealed at 500 ℃ showed a uniform granular structure with an elemental composition near stoichiometric CZTS. Next a buffer layer of ZnS for a heterojuntion solar cell was fabricated using a chemical bath deposition (CBD) technique. The films are well adherent, optically transparent and their band gap energy was found to be 3.6 eV.
파와르,INAMDARAKBAR IBRAHIM,Kishor V. Gurav,신승욱,곽지혜,조용철,윤재호,박희순,권세한,김형상,김진혁,임현식 한국물리학회 2015 Current Applied Physics Vol.15 No.2
We have synthesized an efficient Cu2ZnSn(SxSe1-x)4 (CZTSSe) absorbers by using single-step rapid thermal sulfo-selenization process of sputtered stack metallic precursor (Zn/Sn/Cu) films. The structural and morphological studies confirm that the suitability of the rapid thermal sulfo-selenization process for the synthesis of a CZTSSe absorber without any secondary phases with large grains. The annealing atmosphere with a mixed-chalcogen source enhances the grain growth of the CZTSSe absorber as compared with pure Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) absorbers. The CZTSSe thin film solar cell shows the best conversion efficiency of ~7%.
Effect of Surfactants on PANI Morphologies and Supercapacitive Properties
김영삼,손재상,주해리,INAMDARAKBAR IBRAHIM,임현식,김형상 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10
Surfactant-mediated polyaniline (PANI) samples were fabricated using an electrodeposition technique for electrochemical supercapacitor applications. We investigated the effect of surfactants such as sodium dodecyl sulfate (SDS), polyvinyl alcohol (PVA), ethylenediaminetetraacetic acid (EDTA) on the PANI morphologies. The surfactants act as a template for PANI deposition during the electrodeposition, modifying the PANI morphology. Scanning electron microscope (SEM) images of the pure PANI samples showed a uniform nanocrystalline structure whilst the surfactant-mediated samples showed overgrown cauliflower-like structures. The electrochemical supercapacitive properties (charge-discharge) were studied in a 0.5 M LiClO4 electrolyte. While the capacitance of the pure PANI sample was 240 Fg−1 at a scan rate of 20 mVs−1, it was 199 Fg−1, 106 Fg−1, and 42 Fg−1 for the PANI-SDS, PANI-PVA and PANI-EDTA samples, respectively. The electrochemical stability of the samples was investigated for 1000 charge-discharge cycles by using cyclic voltammetry measurements.
이슬기,김종민,우현석,조용철,INAMDARAKBAR IBRAHIM,파와르,김형상,정웅,임현식 한국물리학회 2014 Current Applied Physics Vol.14 No.3
We fabricate a Cu2ZnSnS4 (CZTS) absorber layer, by using single step electrodeposition of CZTS precursor, deposited at 1.05 V, followed by high temperature annealing in a sulfur atmosphere. X-ray diffraction pattern indicates that the as-grown sample is amorphous in nature, and polycrystalline CZTS thin films with kesterite crystal structure have been obtained by sulfurization from 450 to 580 C. Surface morphologies of the as-grown sample show some voids with agglomerated particles. After sulfurization, the morphologies of the annealed samples become more uniform, and dense. EDAX study reveals that the sulfurized samples are nearly stoichiometric, being Cu-rich and S-deficient in composition. The band gaps of the annealed samples are found to be in the range from 1.9 to 1.5 eV.
샤르마,김보균,Heang-Seuk Lee,최치규,INAMDARAKBAR IBRAHIM,임현식 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10
Nanocrystalline and nanocolumnar aluminum thin films were deposited on glass and Ti/glass substrates at normal and oblique angles of incidence in vacuum (1.0 × 10−6 Torr) by using an electron-beam evaporator. The average grain size of the Al thin films produced at a normal angle of incidence increased from 25 nm to 50 nm when the substrate was changed from glass to Ti/glass. The average aspect ratio of the aluminum nanocolumns (Al nanorods) grown on the glass substrate increased from 1.65 to 3.65 as the deposition angle increased from 65° to 85° while the aspect ratio of Al nanorods grown on Ti/glass substrates increased from 1.80 to 4.00 as the deposition angle increased from 65° to 85°. The X-ray diffraction pattern showed a broad baseline in nanocrystalline and nanocolumnar thin films. In the case of Al thin films on glass, the full width at half maximum (FWHM) was observed to be 14.34 for all depositions while in the case of Al thin films on Ti/glass, the FWHM was decreased from 17.66 to 14.02 as the deposition angle increased from 0° to 85°. The X-ray photoelectron spectroscopy analysis confirmed that the peak for Al nanorods was observed at a binding energy of 74.44 eV.
한재석,손재상,조상은,조용철,김종민,우현석,김연정,INAMDARAKBAR IBRAHIM,김형상,임현식 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.3
Multi-wall carbon nanotube/polyaniline (CNT/PANI) nanocomposite thin films for electrochemical electrode applications are synthesized on flexible graphene-coated indium-tin-oxide (ITO) substrates by using a drop-casting technique. Graphene serves as an adhesion layer between the CNT/PANI nanocomposite film and the flexible ITO substrate. A nanoscale vermicular morphology of PANI films containing well-dispersed CNTs is formed on the surface of graphene. The electrochemical characteristics of the nanocomposite films are investigated in a 0.5-M LiClO4 + PC electrolyte. The electrical conduction of the CNT/PANI/graphene/ITO film is considerably superior to that of a PANI/ITO film. The cyclic voltammogram measurements indicate that the specific capacitance of the CNT/PANI film is 134 F/g which is 11% higher than that (120 F/g) of the pure PANI film. Most importantly, the nominal capacitance loss of the PANI/CNT film (1.2%) is significantly improved relative to that of the pure PANI film (18.1%) after 100 charge-discharge cycles. We attribute the considerably improved capacity retention of the flexible CNT/PANI electrode to the graphene adhesion layer.
Electrical Properties of N2- and H2-annealed Bulk MoS2/Metal Junctions
한재석,이종하,이종경,우현석,김종민,조용철,조상은,김형배,김형상,파와르,INAMDARAKBAR IBRAHIM,정웅,임현식 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.7
We have investigated the electrical transport in symmetric metal-bulk MoS2-metal junction devices as a function of the temperature in the bias-voltage range between −0.5 V and +0.5 V. Three different types of MoS2 were: pristine, N2-annealed and H2-annealed MoS2. Metal/MoS2 contacts were formed by evaporating various metals (Al, Au, Ti and Ni) with different work functions on the surface of MoS2. The two-terminal current-voltage characteristics were measured in the temperature range from 100 K to 300 K, and the thermal activation energies at the metal-bulk MoS2 interface were also estimated. The Au/MoS2 and Ni/MoS2 junctions exhibit Ohmic behavior (linear current-voltage characteristics) over the entire temperature range, regardless of whether N2- or H2-annealing was applied. Al/N2 annealed MoS2 and Ti/N2 annealed MoS2 junction devices exhibited Schottky behavior (nonlinear current-voltage characteristics) as the temperature was decreased below 150 K. We attribute the different electrical transport properties that were observed to the dissimilar natures of the junction interfaces and to the annealing-induced modification in the Fermi level of MoS2.
Drop-casted Polyaniline Thin Films on Flexible Substrates for Supercapacitor Applications
Jongmin Kim,J. Sohn,조용철,Hyeon Seok Woo,Jaeseok Han,조상은,INAMDARAKBAR IBRAHIM,김형상,임현식 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.9
The PANI (polyaniline) thin films are synthesized on flexible ITO/PET (indium tin oxide/polyethylene terephthalate) substrates by using the drop-casting method. The amount of thePANI for the drop casting varies from 0.04 to 0.16 g. The morphology of the drop-casted PANI filmsshows a porous vermicular shape. The electrochemical supercapacitor properties of the PANI filmsare examined in a 0.5-M LiClO4 + PC electrolyte. The PANI films with 0.08 g of PANI show highercurrent density and considerably higher specific capacitance and capacity retention, compared withother PANI films. The highest specific capacitance of the films with 0.08 g of PANI is found to be120 F/g, and the capacity retention is found to be as high as 70.51% after 100 charge-dischargecycles.